The basic oils formulated by oil companies for use as lubricants are monograde oils. The majority of engines such as explosion, gasoline or diesel engines for cars for example, use multigrade oils.
Additives must be incorporated into these monograde oils to obtain multigrade oils after mixing.
These additives, insoluble or non-miscible in oils, are subjected sulphonation reactions in order to be solubilized in the oils to which they are added. With ageing, the oils release acids which corrode engines, more particularly stationary engines.
To avoid corrosion of engines, more particularly of stationary engines, it is thus necessary to increase the frequency of changes or to somehow protect the metal surfaces against corrosion by acids released from the oils.
Moreover, when engines remain unused for a certain period, numerous metal pieces dry out completely, i.e. there is no longer any lubricating fluid film between the metal pieces customarily in motion, and they are no longer lubricated at all at the start of the setting in motion of the engine and for a certain period; a metal-metal contact is then established.
It would thus be desirable to formulate a greasing oil avoiding the drying out of these metal surfaces or at least allow the coating of the metal pieces with a layer of solid lubricant serving as lubricant at the start of the setting in motion of the engine. Such a solid lubricant should also be fixed on the totality of the metal surfaces to be lubricated.
French patent application no. 2 359 200 describes a hybrid lubricant dilutable in a conventional fluid greasing oil, comprising a colloidal aqueous dispersion of polytetrafluoroethylene particles, a neutralizing and stabilizing agent, a carrier fluid lubricating oil incorporated in the stabilized dispersion to form with it an emulsion, which emulsion includes a dispersing agent and finally a wetting agent added to the emulsion and endowed with affinity vis-a-vis rubbing surfaces so as to predispose them to be impregnated by the said particles and fuse with them to form a superficial lubricating layer.
However, the hybrid lubricant uses an aqueous dispersion. The presence of water is prejudicial to the lubricating effect of oils, above all at the high temperatures where it is vaporized, involving difficulties of circulation in its circuit.
European patent no. 0 293 427 relates to a process for producing a dispersion of polytetrafluoroethylene for use as a lubricating oil or as an additive to the latter. In this process, a non-ionic surface agent is fixed to the polytetrafluoroethylene particles by heat treatment in several zones or stages of decreasing temperatures including a first zone at very high temperature, the first high temperature being prejudicial to the quality of the oil.